1. Field of the Invention
This invention relates to an ophthalmologic knife for widening a highly self-sealing incision formed at an eyeball to a width required for inserting an intraocular lens.
2. Description of Related Art
When performing ophthalmologic surgery for a cataract, a primary incision is formed at the cornea or between the cornea and the sclera, and a vacuum nozzle of a phacoemulsification device is inserted into the primary incision to extract the cloudy portion of a crystalline lens. In such case, the primary incision is formed with a width within the limit for inserting the vacuum nozzle so as to prevent intraocular fluid leakage. After a particular portion of the crystalline Tens is extracted, an intraocular lens is inserted; in such case, typically, the necessary width of the incision for such insertion is larger than the width of the primary incision, and a secondary incising for widening the primary incision is performed.
When incising is performed upon the cornea or between the cornea and the sclera in an ophthalmologic operation, a suture or a ligature of the incised cornea and the sclera is required. However, with such suture process, the sutural thread would pressure the cornea and the sclera to result to possibilities such as delay in vision recovery or causing of astigmatism; therefore, recently, instead of such suture, surgery is performed generally by forming an incision of a self-sealing nature, in which the incision could seal by itself.
An incision of high self-sealing nature formed during the vacuuming of the crystalline lens will be explained with reference to FIG. 7. As shown in FIG. 7(a), when a cornea 52 is incised diagonally in a thickness direction with a knife 51 (Normally, looking from the front of the eyeball, the incising is performed by inserting the knife 51 diagonally upward from below), as shown in FIG. 7(b), an inner pressure of the eyeball works upon the cornea 52 in a widening direction (the direction where the cornea 52 is emerged as indicated with an arrow a) so that the incised portion of the cornea 52 would be pressed together and sealed for forming an incision (primary incision) 53 of high self-sealing nature. Such primary incision 53 would have the minimal width to enable insertion of the vacuum nozzle of the phacoemulsification device for vacuuming the crystalline lens.
In a case where an intraocular lens is inserted after a particular portion of the crystalline lens is extracted, the width of the primary incision 53 is typically smaller than the necessary width for inserting the lens since the width of the primary incision 53 is the minimal width for inserting of the vacuum nozzle. Therefore, the width of the primary incision 53 is required to be widened to a width corresponding to the measurement of the intraocular lens. Since there is a risk of damaging the unaffected portion of the crystalline lens with a front tip of the knife 51 when attempting to widen the primary incision using the knife 51 for incising the eyeball, a special knife having a front tip portion without any cutting edge is typically used.
An example of a knife used for widening the primary incision 53 will be explained with reference to FIG. 8 and FIG. 9. In the drawing, the knife 55 has a width narrowing toward its front tip portion, and is provided with cutting edges 55a formed on both sides. The front tip portion has a flat surface 55b formed substantially perpendicular to the axis of the knife 55. A slope 55c is formed at a topside of the front tip portion, in which the slope 55c is connected with the flat surface 55b. Accordingly, a cutting edge capable of incising the eyeball is not formed at the front tip portion of the knife 55, and an obtuse edge 55d with an angle no less than 90 degrees is formed in which the obtuse edge 55d is formed with the flat surface 55b contacting to a rim portion of the cornea 52 comprising the primary incision 53, and the slope 55c connecting to the flat surface 55b. 
As shown in FIG. 10, when widening of the primary incision 53 is attempted by inserting the knife with the flat surface 55b and the obtuse edge 55d into the primary incision 53 formed at the cornea 52, due to the high self-sealing nature of the primary incision 53, the flat surface 55b of the knife 55 would contact and be caught to the rim portion of the cornea comprising the primary incision 53 to raise a problem of preventing the knife 55 from being inserted smoothly into the primary incision 53.
Along with such problem, there are risks as scraping the eyeball with the flat surface 55b of the knife 55 or damaging the cornea 52 by rolling the cornea 52 upward, and further, increasing the burden of the physician.
When using a knife formed with a cutting edge on a front tip portion to avoid such problems, problems such as the risk of newly incising the surrounding of the primary incision or affecting the self-sealing nature of the primary incision would be created.
It is an object of this invention to provide an ophthalmologic knife capable of being easily guided inside when widening a highly self-sealing incision formed at the eyeball, without a risk of damaging the cornea surrounding the incision or the crystalline lens.